I have a question about adding more capacitive touch sensors through a multiplexer. I'd like to add a bunch more sensors providing continuous data (i.e. not digital on-off buttons). The tests I've made make me concerned that I won't be able to get smooth, consistent data when reading this through a multiplexer (MC14067). I understand that with wires dangling and a breadboard one can pick up stray capacitance so it's not the best test but my tests have led me to be concerned anyway and I thought I'd ask if anyone can confirm the possibility (or impossibility) of this technique before I go through all the effort of getting a PCB made.

Here's the situation:

1) Connecting a sensor and the resistor directly to the Arduino pins produces smooth, continuous data as my finger moves across the sensor (as long as there's some insulation over the copper - scotch tape has worked fine for my prototypes).

2) Connecting the sensor and resistor into a breadboard and then on to the Arduino also produces smooth, continuous values (though slightly different than number 1).

3) Connecting the pins through a multiplexer to read multiple sensors produces approximately accurate results but the values jump around a bit. That is, it won't be completely random but with a constant finger position it will jump back and forth within a small range. Too much change to use smoothing in the code I think.

The fact that both 1 and 2 work well leads me to believe that it's the multiplexer, not the breadboard/dangling wires that is causing the problem.

P.P.S - Well, I just figured something out. If I reverse the order of the HIGH-to-LOW and LOW-to-HIGH transition sections, I get much smoother results. Still not quite as smooth as without the multiplexer, but I'm more optimistic about getting this to work.

Hi, A guy named Terry Fritz did some work on using multiple capacitance sensors together. It's not exactly an answer to the multiplexer question, but it could be helpful. I'm not techy enough to know exactly how, but he found a way to clean up and amplify noisy signals from the antennas.Check it out: http://thereminvision.com/version-2/TV-II-index.html

I've potentially saved a HELL of a lot of money coming across this forum! I'm wanting to toggle a switch like you would with one of those tactile lamps that you touch a few times to get different degrees of intensity. What I'd really, REALLY appreciate would be if someone pointed me in the right direction for achieving this using Max/MSP as the programming language (I'm using 'simplemessagesystem' to interface the Arduino with Max). Would it be too much of a challenge?

I'm a rookie to this Arduino game but I got this code working and it suits my project really well. However, I don't need to read various degrees of pressure, I merely need an on/off register. I know I need to add a boolean but I have no idea where... Any ideas?

i'm trying to do the same. i was initally using the capsense code but abandoned it because i couldn't seem to create multiply capacitive sensors from it. i'm not that hardcore a programmer you see.

instead, i found this code http://www.arduino.cc/playground/Code/CapacitiveSensor

which works perfectly in arduino, the numbers are outputting and i'm trying to use with the arduino2max patch but no joy. as the pins are declared in the arduino code, surely the max patch should read the digital pins? any help is really appreciated.

I'm currently building a capactive measurement system as part of my PHd, I've found, depending on what accuracy you want, that the best way is to use a sigma delta modulation technique. You can find this in Analog Devices AD774x series of Capacitive to Digital Converters. These chips go from one channel to 12 channels for mounting capacitive electrodes and have resolutions between 8 and 24 bits over full scale ranges of around 25pF with a bit of calibration, obviously, that gives a lot of sensitivity.

The chips communicate with a host through the i2c bus, so you ca use Arduino's wire library to get the data out of the slave chip (I sweated over a prototype function for a PIC i2c protocol for months when I found arduino!) and use that to manipulate the data anyway you want.

the only thing is that these chips are only available in TSSOP form so can be a bit of a pain in the arse to solder, however it's quite a nice solution as I am finding out.

You are correct that the guard pin doesn't do much and can easily be omitted. This was a klugy way to implement a technique which is used with op amps and other high impedance (low current) circuits.

You can now use the [[http://www.arduino.cc/playground/Main/CapSense| capSense library]] and use any pins you want. The results will vary a bit from pin to pin though.

But if you do want to make the wire insensitive and only the foil at the end sensitive, use shielded audio wire and ground the shield on the duino end only. (Make sure the shield on the other end doesn't touch the sensor, or it won't work.